The present invention relates to crushable structures configured for energy absorption and energy management such as during a vehicle crash.
Vehicle components are designed to reduce property damage and provide safety to the occupants of an impacted vehicle through energy management.
Energy management is typically accomplished by designing vehicle components for predictable and repeatable deformation. In low-speed impacts, components such as bumpers and bumper brackets are designed to absorb significant amounts of energy when impacted via deformation of these components. For higher-speed impacts, the vehicle chassis is designed to absorb energy by deforming. Side impacts also use deformable components such as sills, rocker panels, pillars and door impact beams. One main difference between the side impact components and those components located on the front or the rear of the vehicle is in how they are designed to absorb energy via deformation. The side impact components absorb energy via deformation associated with side-bending-type shape change of the components. Frontal and rear components such as bumper brackets and chassis components are designed to crush in an accordion fashion in a direction parallel to the impacting force. In frontal and rear impacts, the collision is either between a moving vehicle and a fixed object (wall, barrier, pole, tree, etc.) or between two moving vehicles. The impact energies are typically high due to speeds and crash dynamics. Chassis components must be able to deform in a predictable and repeatable manner to provide safety to the occupants and reduce property damage.
Different types of component failure will produce different response curves and varying degrees of efficiency in terms of how the energy is absorbed. Impact energy absorption is calculated by multiplying a force of impact resistance times the impact stroke of a component. A component having a high efficiency of energy absorption is generally described as a component that upon impact jumps quickly to a desired resistance force and then maintains (“holds”) that force and thus absorbs a desired maximum amount of energy continuously over a desired maximum stroke distance. A tubular structure that bends over when impacted in a near axial direction has absorbed energy, but has not done so in a very efficient manner. A more efficient response would be had if the tube folded on itself in an accordion fashion. The accordion-type deformation provides the greatest amount of energy absorption within the provided package space. The final deformed piece represents the smallest packaging space of stacked material. The described innovation defined in this write-up is a crushable tubular structure that when impacted in a near axial direction, will collapse on itself in an accordion fashion. This innovative design can be scaled for small applications such as a bumper bracket or for larger applications such as a chassis component.
The use of tubular structures for both chassis components and/or bumper brackets is nothing new. These types of tubular structures have been used on many various components throughout the vehicle. Most applications with these types of tubular structures coincide with protection from axial and near axial impacts. There are various manufacturing processes that are capable of producing tubular structures that when impacted in a near axial direction, will collapse on itself in an accordion fashion. The complexity and inherent cost associated with the manufacturing processes tend to increase as the energy management efficiency of the design increases. Manufacturing processes capable of producing tubular structural components and ranked by cost from high to low include hydro-formed, clamshell designs fabricated from two stampings spot-welded together, deep-drawn stamping, simple expansion using internal mandrels, and simple roll-formed tubular designs with crush initiators. Tubular components can be formed by hydro-forming processes into complex shapes having non-uniform cross sections that vary along their length, where the non-uniform cross sections are tailored for particular needs and properties, such as for energy absorption. For example, vehicle frames often include hydro-formed components. However, hydro-forming processes are expensive, messy (since they involve placing a fluid within a tube and then pressurizing the fluid), and tend to require relatively long cycle times. Further, they become generally not satisfactory when higher strength materials are used, such as High-Strength-Low Alloy (HSLA) materials, and/or Advanced-Ultra-High-Strength Steel (AUHSS) materials, since these materials are difficult to form, have low elongation and poor formability, and tend to wear out tooling quickly. Further, higher strength materials often tend to kink upon impact, which leads to localized bending at minimal points (and not widespread and multi-point bending and “crushing”), which in turn results in premature catastrophic failure and lower energy absorption as well as less predictability of energy absorption during impact.
Some current processes for forming crushable tubes use hydro-forming processes. However, hydro-forming processes are expensive and capital intense, since liquid must be captured within the part and then pressurized. Capturing liquid within a part sufficiently for high pressure is difficult, time consuming, required expensive tooling, and is generally messy. Further, hydro-forming is limited to approximately 15% expansion of material over the length of the part. Further, hydro-forming is limited in the types of materials that can be used. The hydro-forming process has been used in the past to produce chassis frame rail tips. However, the process is slow and typically restricted with the use of higher grade materials due to the inability to move material with the internal fluid pressure.
Another potential process for forming crushable tubes is stamping, where two clamshells are stamped and then welded together. However, the overlapped weld seam associated with a clamshell type design is not desirable due to the amount of weld, heat and weight added to the part. Further, fixturing of the parts, welding, and secondary processing is expensive and requires significant “extra” handling of parts. Further, the overlapped flanges that are welded together result in wasted material, and further can lead to undesirably strong regions on the parts. Apertures can be added to stamped crush tubes to promote the accordion crush of the part. However, this may require the process to utilize a progressive die and a considerable increase in tonnage to accommodate the large number of piercings. Stamping is also limited in the grades of material that can be stamped due to the rapid forming associated with the process. Higher grade materials with high physical properties and low formability are incapable of being stamped due to the large amount of forming associated with the stamping process and due to tool wear and abuse from the (high strength) materials.
It is desirable to provide a crushable structure that can be made from high-strength steels, yet with reasonable cost and that will crush during an impact with excellent repeatable and predictable results. Thus, a component, and apparatus and method of manufacturing same having the aforementioned advantages and solving the aforementioned problems is desired.